A control system typically comprises one or more physical system components under some form of automated control that cooperate to achieve a set of common objectives. The control system may be designed to reliably control the physical system components in the presence of external disturbances, variations among physical components due to manufacturing tolerances, and changes in commanded input values for controlled output values, such as a cement mixture density, for example. The control system may also be designed to remain stable and avoid oscillations within a range of specific operating conditions.
In a well bore environment, a control system may be used when mixing materials to achieve a desired mixture output. For example, when drilling an oil or gas well, it is common to install a tubular casing into the well bore and cement the casing in place against the well bore wall. A mixing system that supports well bore servicing operations, such as cementing casing into a well bore, may be designed with a control system configured to provide a desired volumetric flow rate of mixed cement having a desired density. In particular, the cement mixing control system may control actuators that allow the in-flow of dry cement material and water to obtain the desired cement mixture density and desired cement mixture volumetric flow rate. The control system may operate, for example, by monitoring the cement mixture flow rate and density, and by regulating an in-flow water actuator and an in-flow dry cement material actuator. Likewise, a fracturing fluid mixing system of similar structure may be employed to mix fluids for fracturing a formation during well completion and/or well production operations. A fracturing fluid mixing system may be designed with a control system configured to provide a desired volumetric flow rate and a desired density of mixed proppant and carrier fluid and optionally other solids and/or fluids suitable for fracturing a formation. The fracturing fluid mixing control system may control actuators that allow the in-flow of proppant material and carrier to obtain the desired fracturing fluid mixture density and desired fracturing fluid mixture volumetric flow rate. The control system may operate, for example, by monitoring the fracturing fluid mixture flow rate and density, and by regulating an in-flow carrier fluid actuator and an in-flow proppant actuator.